A. Field of the Invention
This invention is related to the technology presently known as Internet telephony (sometimes referred to in the art as IP Telephony, where IP stands for Internet Protocol) and the process by which digitized voice is treated as data and transmitted across a digital data network between the calls' participants. More particularly, the invention relates to a method and protocol by which a plurality of IP Telephony Gatekeepers may organize themselves into a hierarchy such that one of the Gatekeepers is elected as an active Gatekeeper and designated to respond to gatekeeper request messages, with the other Gatekeepers remaining in a standby mode.
B. Description of Related Art
Internet telephony presents an attractive alternative for long distance telephone calls, as compared to the public switched telephone network (PSTN), which has been the traditional transmission medium. The primary advantage is cost. Long distance service providers for the PSTN offer domestic services at rates ranging from roughly 10 to 30 cents per minute, and international rates for substantially more, depending on the time of day, day of the week, and the distances involved. In contrast, the cost of Internet telephony anywhere in the world is potentially the cost of a local telephone call to the local Internet telephony provider at one end and the cost of a local call from an Internet telephony service provider at the far end to the destination telephone. Once the call is routed from the local Internet telephony provider onto the Internet, the transmission of the data from the local Internet telephony provider to the far end Internet telephony provider is free for all practical purposes, regardless of where the two parties are located. The same holds true for whether the call is sent over the Internet or over a private data network.
Internet service providers are generally believed to be a suitable entity to provide Internet telephony services. Such entities generally have equipment that can be used for performing the function of placing and terminating calls on the Internet: i.e., a Gateway or Terminal in accordance with the H.323 and H.225 ITU-T Standards. The ITU-T H.323 and H.225 Standard documents, presently in a draft form, are both hereby fully incorporated by reference herein.
More particularly, the function of a Gateway/Terminal can be preformed in the same devices that are used by most Internet service providers for Internet access. These devices are known in the art as Network Access Servers or Remote Access Servers. Such devices are commercially available from 3Com Corporation and other telecommunications equipment manufacturers such as Ascend Communications, Lucent Technologies (successor to Livingston Enterprises), and Multitech.
A representative Network Access Server is the Total Control Enterprise Network Hub from 3Com Corporation, described in the patent of Dale M. Walsh, et al., U.S. Pat. No. 5,528,595, which is fully incorporated by reference herein. This device has a telephone line interface that is connected to a high-speed multiplexed digital PSTN telephone line, such as a T1 line. The device further provides a plurality of digital modems to perform signal conversions on the data from the telephone line channels and a bus network connecting the modems to a network interface card or module. The network interface couples the device to a local or wide area network, such as the ISP backbone network, corporate LAN or WAN, or the Internet. These types of devices can be used in Internet telephony as described herein.
FIG. 1 depicts one possible embodiment of a basic IP telephony scenario. An Internet telephony call can take place with the calling party either using a conventional telephone 10 or a personal computer 12 equipped with a modem, speaker and microphone, and a suitable commercially available telephone software program such as Megaphone .TM.. The call is transmitted over the local Public Switched Telephone Network (PSTN) 14 (typically as a local call) to an Internet Service Provider (ISP) Gateway/Terminal 16. The ITU-T H.225/H.323 specifications provide further details (not important here) concerning the functions of the Gateway/Terminal 16. The call is then routed onto the Internet 18 and forwarded to a Gatekeeper 20 in accordance with the H.323 and H.225 standards. The Gatekeeper 20 may be embodied as a general purpose computer, or as one function performed by an existing piece of telecommunications equipment such as a network access server. The Gatekeeper 20 determines where to send the call over the Internet 18' to the proper terminating ISP Gateway/Terminal 23 for the called party. The terminating Gateway/Terminal 23 calls the called party over the PSTN 14', either to a conventional telephone set 22 or to a PC 24, and facilitates communication between either the telephone 10 or computer 12 at the near end with the telephone 22 or computer 24 at the far end.
There are 3 types of calls that can be made with Internet telephony:
1. PC to PC (PCPC): This type of call has both users sitting at their personal computers (PCs). The PCs have handsets or microphone units which takes the speech and digitizes the speech. PA0 2. PC to Telephone (PCTL): This type of call allows a PC user to call the other party on their telephone. PA0 3. Telephone to Telephone (TLTL): This type of call allows for both parties to use a telephone. For all three types of calls, the call is carried for free over the Internet for the bulk of the distance between the users. The public switched telephone network is used only at the ends, i.e., at 14 between the calling party and the local Internet service provider, and at 14' between a call termination gateway and the called party at the far end. In most cases, these calls will ordinarily be local calls with no long distance telephone charges associated therewith. In contrast, a conventional telephone call is routed entirely over the PSTN, and if the call is over a substantial geographic extent substantial per-minute long distance charges will accrue for the person that initiated the call. PA0 1. A calling party dials (via telephone 10) over the local PSTN 14 the number of their Internet telephony company's Gateway/Terminal 16. (This is similar to the way a pre-paid calling card works today.) The initiating Gateway/Terminal 16 is typically a Remote Access Server such as described above, or some other similar product or system that couples a telephone line to a packet switched data network 18. PA0 2. The same party then dials the number of the desired party (i.e., the call recipient at 22 or 24) for the initiating Gateway/Terminal 16 to use to connect the call over the Internet 18. PA0 3. The initiating Gateway/Terminal 16 has prior knowledge as to which node on the network (i.e., Gatekeeper 20) is it supposed to use to get closest to the call recipient's area code. Alternatively, it sends out a gatekeeper request message seeking a Gatekeeper to handle the call. In accordance with the H.323 specification, in any one particular defined region or "zone" (described more hereafter), only one Gatekeeper may respond to the gatekeeper request message. A Gatekeeper in the zone answers the gatekeeper request message with either a gatekeeper accept message or a gatekeeper reject message, depending on whether the Gatekeeper is the active Gatekeeper in the zone. PA0 4. Assuming that the initiating Gateway/Terminal 16 receives a gatekeeper accept message from the Gatekeeper 20, the initiating Gateway/Terminal 16 now asks for connection information from the Gatekeeper 20 on behalf of the call. PA0 5. The Gatekeeper 20 sets up the call with the proper terminating Gateway/Terminal 23 for the call recipient. For example, the call recipient may have an Internet service agreement with a local Internet service provider operating Gateway/Terminal 23. The terminating Gateway/Terminal 23 in this example comprises a network access server maintained by the Internet service provider a few miles from the call recipient's residence. PA0 6. The Gatekeeper 20 then provides the routing information necessary for the initiating Gateway/Terminal 16 to send its data to the terminating Gateway/Terminal 23. PA0 7. The terminating Gateway 23 then places a call over the PSTN 14' to the called party and then sends the call data from the Internet 18 to the called party. The PSTN converts the digitized voice back to audio for the called party's telephone.
In a representative proposed implementation of IP telephony, the following sequence of events occur:
Implementation of the above, somewhat simplified, example requires the solution of some difficult problems that are not addressed in the H.323 and H.225 standards documents, and, to the knowledge of the present inventors, have not been solved by those working in the art. For one thing, in any particular region or H.323 "zone" (which may be a building, a city block, or some other discrete area in which a network or group of networks are bounded either geographically, logically, or by ownership of networks), the H.323 standard specifies that one, and only one, Gatekeeper (i.e., Gatekeeper 20) is supposed to respond to Gatekeeper request messages from initiating Gateway/Terminals. In actuality, there may be several, even many Gatekeepers in the region or zone. In the present state of the art, the individual Gatekeepers may not be aware of each other, or know whether the other Gatekeepers are active (i.e., designated to respond to gatekeeper request messages) or even on-line at any given instant. This is particularly so if the H.323 "zone" is a geographic region that incorporates networks owned by two or more different entities. Furthermore, over time, the number of Gatekeepers in the zone and their status will change repeatedly, and without any manner of predictability of knowing which Gatekeepers will be on-line and which Gatekeepers will be active.
Given this situation, several problems can occur: (1) more than one Gatekeeper in the zone responds to an active gatekeeper message, in violation of the standard; (2) the active Gatekeeper may go down due to technical problems or due to graceful shut-down by the system operator, and the remaining Gatekeepers do not whether to respond to active gatekeeper claims; and (3) new Gatekeepers may come on line and will not know whether or when they should respond to active Gatekeeper request messages.
The present invention addresses these problems. It provides a method and protocol by which Gatekeepers in a zone may perform an orderly ranking of each other with respect to all the other on-line Gatekeepers that are in the same zone. The above-referenced problems are expected to be minimized or not occur, resulting in an improvement in the efficiency and efficacy of routing telephone calls over the Internet.